Voltage rises in the electric supply of lighting networks have very detrimental effects, on the expenditure of energy consumed, as well as on a notable reduction of the life of lamps. These instabilities tend to take place when there is less consumption, and coincide precisely with the time when the street lighting operates.
On the other hand, it has been verified that it is possible to slightly reduce the luminous flux supplied to the streets when there is less traffic and less people, without any deterioration in the quality of the lighting or, therefore, of the safety of streets.
This reduction of luminous flux is basically carried out by means of two systems: reduction in each light spot or generally in the head of each lighting sector.
Adjustment in the light spot is done by means of the installation, in each luminaire, of special double level reactors switched by a relay. The operation of this relay can be done from the control panel of the lighting sector by means of special wiring, or else by installing an electronic timer in each light spot. If it is done from the control panel of the sector, there is the inconvenience of the need for additional wiring, while, if it is done by means of a timer, there is the inconvenience of the difficulty and little flexibility in programming each individual timer.
Adjustment at the head of the feed voltage of an entire sector is done by means of autotransformers whose dimensions and weights are very high, which implies a serious difficulty for the installation in control panels. Additionally, the presence of moveable electromechanical components reduces the reliability of equipment that is to operate in adverse environmental conditions.
All of this has brought about the development of static adjustment equipment with such advantages as the absence of moveable parts, a smaller size and lighter weight, lower cost, and more rapid, more versatile control.
Up to now, the static equipment designed for this purpose has suffered from inconveniences that have hampered the operation thereof. On the one hand, the systems used to adjust incandescent lamps or, in general resistive loads, and based on the phase control of a triac or of the thyristors mounted antiparallel, cause a significant deformation of the current waves, which, in the case of discharge lamps, result in the malfunctioning of the lamps and even the untimely switching off thereof. On the other hand, the power factor of the installation is considerably worsened and variably depends on the adjustment spot, which makes it very difficult to balance it by means of compensation.
Other recent innovations are covered by the following patents:
U.S. Pat. No. 4,924,150 "POWER-LINE CONTROL SYSTEM," teaches a device that is inserted between the feed source and the load and that permits the control of the waveform of the current supplied, but without any contribution or reduction of active energy.
In other words in that system, the inverter placed between the feed and the load does not contribute to or absorb net energy from or towards the d.c. feed thereof, without the energy absorbed in certain parts of the feed cycle being returned in others, for the purpose of controlling the waveform of the current.
French patent 2,668,674 "CIRCUIT DE REGLAJE D' INTENSITE LUMINEUSE POUR INSTALLATION D'ECAIRAGE UTILISANT DES LAMPES OU TUBES A DECHARGE," teaches an adjustment system comprised of a three-phase transformer series connected between the feed phases and the load. The secondary of this transformer is connected to a diode rectifier, that provides continuous current, which, by means of a thyristor controlled bridge, is returned to the input through some reactors. This assembly, according to the specification of said patent, varies the effective value of the voltage delivered to the lamps, but maintains the crest value constant.
The most important technical differences of the regulator proposed with regard to these two systems are the following: